Typically, wheel ends are manufactured separately and independently from the drive assembly and, as a result, the wheel end and drive assembly typically comprises separate systems that are fluidly sealed from one another. In some situations, the separate manufacturing of the wheel end and drive assembly allows machine designers some flexibility in selecting the appropriate combination of wheel end and drive assembly units based the size and desired function of the machine.
Often, however, the flexibility provided by such separate manufacturing of the wheel end and drive assembly comes at the expense of the size and material cost associated with the drive system. For example, in order to properly modify the structure of a drive assembly to fit a particular wheel end (or vise versa), a customized adaptor may be required. Such adaptors may significantly increase manufacturing and production costs associated with the machine. Furthermore, customized adapters may unnecessarily add to the weight and overall footprint of the drive, thus decreasing machine power/weight ratio. Therefore, in order to reduce or eliminate manufacturing and production costs of wheel ends and drive assemblies, as well as limit the weight and footprint of the drive assembly, a wheel end with a fully integrated drive assembly may be required.
One system that integrates a hydrostatic wheel end and drive assembly into a single unit is described in U.S. Pat. No. 6,186,262 (“the '262 patent”) to Mann et al. The '262 patent discloses a hydrostatic wheel drive having a radial piston motor, a planet gear drive assembly, and an integrated brake that, when activated, prevents rotation of the radial piston motor, thereby prohibiting rotation of the wheel drive. The hydrostatic wheel drive of the '262 patent also comprises a cover with integrated valves for adjusting fluid connections of certain cylinders of the radial piston motor between. For example, the valves may be selectively operated to fluidly couple one or more cylinders in parallel (thereby increasing displacement) for low-speed machine applications. Alternatively, the valves may be selectively operated to fluidly couple one or more cylinders in series (thereby increasing displacement), which may be advantageous for machine applications requiring operation at low to moderate speeds.
The motor of hydrostatic wheel drive described in the '262 patent is on a separate fluid circuit from the final drive assembly, thereby requiring separate hydraulic fluid circulation systems—e.g., one for circulating hydraulic fluid for operation of the motor and one for circulating oil for lubricating the drive components (e.g., gear units, etc.) Consequently, machines that rely on multiple hydraulic systems for operating the drive pump/motor assembly and lubricating the final drive components may require multiple filters, conduit systems, reservoirs, etc., significantly increasing material costs for each wheel assembly. Moreover, because each hydraulic system requires separate periodic maintenance (e.g., fluid/filter change, inspection, etc.), maintenance costs and repair times associated with machines such separate maintenance may be substantial.